1. Field of the Invention
The present invention relates in general to explosive devices including pyrotechnic devices, munitions, and rockets which utilize a detonator assembly and, more particularly, to a detonator formed entirely from insensitive energetic compositions, and to a method of making same.
2. Background Art
Under their normal condition of use, modern munitions are both effective and relatively safe, and they are unlikely to explode or burn spontaneously despite the fact that they are composed primarily of energetic material. The energetic materials, i.e., high explosives, gun propellants, rocket propellants, etc. found in munitions of all types are sensitive to heat and to mechanical shock. Consequently, they can be triggered by fire or by impact with bullets or fragments.
A range of energetic materials can be used in low-risk munitions: explosives and propellants less vulnerable than their predecessors to both slow and rapid heating (cook off) and to impact by bullets or fragments of exploding shells. For gun propellants, the single, double and triple base formulations now in service can be replaced by others based on components that are more energetic but less sensitive. In the case of warheads, efforts are being made to replace explosives such as TNT, which is very sensitive to heat and shock, with a more stable plastic-bonded explosives which are better able to withstand adverse conditions. These new explosives and gun propellants are made primarily with energetic crystals such as RDX and HMX, contained in new energetic binders and plasticizers.
An insensitive munition (IM) is one that will not detonate under any conditions other than its intended mission to destroy a target. If it is struck by fragments from an exploding shell or struck by a bullet, it will not detonate. Also, it will not detonate if it is in close proximity to a target that is struck. Further, in extreme temperatures, the munition will only burn without creating/generating an explosion or a detonation.
To reduce the chance of accidental explosions or fires, the U.S. military is interested in replacing existing main charge explosives with newer more insensitive explosives such as PBXN-103 and PBXN-109. Existing booster explosives and fuses have insufficient energy output to reliably initiate the new insensitive main charge explosives. The existing Department of Defense inventory of fuses and booster explosives is very large and cannot be replaced without considerable cost. What is needed is an inexpensive method of reliably initiating the new, more insensitive main charge explosives while at the same time reducing the chance of an accidental initiation of a fuse or detonator system.
The U.S. Department of Defense is interested in reducing weapon vulnerability and improving weapon safety in extreme and abnormal environments. Insensitive munitions are one way to achieve these goals. A fuse train is needed that will ignite these insensitive munitions at extremes of temperature, but will not compromise the insensitivity of HE main charge fill to external threats (U.S. Pat. No. 5,275,106).
U.S. Pat. No. 5,567,912 discloses that insensitive munitions are prepared by making an energetic composition, processing the composition into intermediate shapes and fabricating an article from the intermediate shape. The article may itself be directed to military use such as a munition or ammunition, and it may also be directed to civilian uses such as demolition charges. In these applications, the explosive is formed into an article that will have blasting effects when exploded. The explosive article is assembled along with other items, such as propellants, fuses, guidance systems, etc. into the munition. The munition can be a small caliber bullet, a large caliber shell, a warhead, a rocket, a bomb, a mortar, a hand grenade, torpedo, mine or similar device. It can be loaded into a weapon such as an artillery piece, a tank or armored vehicle.
U.S. Pat. No. 5,567,912 also discloses that an insensitive munition may be formed from crystalline heterocyclic nitramines HMX and RDX. These materials have very high energy densities and are well known in the field. They have been used in ammunitions and munitions for over sixty years and a very large body of data have been developed for their manufacture and safe use in munitions in both propellants and explosives.
HMX and RDX have been type classified and described with military specifications in most countries in the world. HMX has a higher energy density than RDX. These materials are available in the form of fine powders.
A conventional explosive is illustrated in FIG. 1 and includes a conventional melt poured or pressed main charge shown generally at 1 which may or may not be formed from an insensitive munition. Detonation of the main charge is effected by means of a detonator 3. The detonator is initiated by a fuse 5 in the form of a shock cord. The shock cord 5 in turn initiates detonator 3, which includes lead styphnate 7, which in turn initiates an adjacent charge of lead azide 9, which in turn initiates a charge 11 of RDX. The detonator energetics are Non-Insensitive Munitions (IM) compliant due to the presence of lead styphnate 7 and lead azide 9. In the embodiment shown in FIG. 1, detonator 3 is initiated via shock cord 5 or other fuse means, which starts the energetic train from lead styphnate 7 to lead azide 9 to RDX 11, which finally has the shock energy and velocity to detonate main energetic 1.
Even though a main charge in a pyrotechnic device may be an insensitive energetic, detonators employing lead azide and lead styphnate are in fact very sensitive to shock, friction and static discharges, even from the human body. Both of these lead compounds have a very high explosive detonation velocity of about 5200 meters per second. Moreover, lead azide has an auto ignition of 350° C., and lead styphnate has an auto ignition of 330° C. In addition, as with other lead containing compounds, both lead styphnate and lead azide are inherently toxic to humans if ingested, i.e., they can cause heavy metal poisoning.
In addition, lead styphnate and lead azide are highly sensitive and are usually handled and stored under water in insulated rubber containers. They will explode after a fall of no more than about six inches or in the presence of a static discharge of 7 millijoules. These properties make these materials highly dangerous and expensive to use in manufacturing pyrotechnic devices. For these reasons, a detonator which is effective without the use of lead azide, lead styphnate, or any other highly sensitive explosive material is needed in pyrotechnic devices, especially those having a main charge of insensitive energetic.
Current detonator designs used in many types of munitions are also illustrated in FIG. 2. These detonators in FIG. 2 have been available for many years and represent the current military and commercial standard. There are several designs that are fabricated and include M2, M10 and M14 detonators. These are typical detonators units that have a wide industrial and commercial usage. In the design in FIG. 2 shown generally at 13 is a shock cord 15 which initiates detonation of the lead styphnate 17, which in turn detonates the adjacent lead azide 19, which in turn detonates an RDX charge 21, which in turn detonates the main charge (not shown).
The current design in FIG. 3 of hand grenades shown generally at 23 includes a fuse assembly which is similar to a detonator assembly as previously described above, except the shock cord is replaced with a primer 25 and delay mix 27. In this conventional hand grenade 23, the handle 29 is pulled away from the body 31 of the grenade 23 to initiate detonation of the primer 25. The primer then initiates detonation of delay mix 27, which in turn initiates detonation of lead styphnate 33, which in turn initiates detonation of lead azide 35, which in turn detonates an adjacent RDX charge 37. It is the RDX charge 37 which initiates detonation of the main energetic filling 39 in body 31 of hand grenade 23.
The RDX charge in current detonators is formed by compaction of the powder or granular RDX. This process is carried out by forcing powdered or granular RDX into a die cavity by means of a mandrel to compress and compact the RDX powder.
It is therefore an object of the present invention to provide a detonator for insensitive high explosives.
It is a further object of the present invention to provide a fuse train for insensitive high explosives which is free of either lead azide or lead styphnate.
It is a still further object of the present invention to provide an insensitive fuse train capable of initiating insensitive munitions at extreme temperatures and without the use of a sensitive high explosive like lead azide and/or lead styphnate.
It is further another object of the present invention to provide insensitive munitions which cannot be initiated by various stimuli including cook-off (high temperatures), bullet/fragment impacts, and shape charge impacts.
In view of the aforementioned drawbacks associated with the use in detonators of lead azide and lead styphnate, there remains a need in the art for an improved detonator system which is safe and reliable and insensitive to shock, radio waves and heat for initiating a main charge of insensitive explosives.